Evaluation of energy recovery potential in wastewater treatment based on codigestion and combined heat and power schemes

Abstract

The future goal for wastewater treatment industry is to transform existing wastewater treatment plants (WWTPs) into water and energy recovery facilities (WERFs). The first step to reach this goal is to achieve energy-neutral or energy-positive status in its operations. This research study develops a systematic quantitative analysis to assess the performance of different wastewater treatment scenarios. The effects of the influent wastewater strength (or concentration), plant capacity, primary treatment efficiency, and different supplemental feedstock have been evaluated to assess the potential for energy recovery in WTTPs. Further, energy performance of the WWTP is optimized using different combined heat and power (CHP) schemes. For the first time, a quantitative mass and energy balance methodology was used to evaluate carbon and energy balance and combined heat and power system optimization. Increasing the primary treatment efficiency, process equipment upgrades, and use of supplemental biodegradable organic waste are identified as influential factors. Increasing the removal of chemical oxygen demand (COD) by 10% in primary treatment resulted in an estimated reduction in total energy requirement by 8.5% and increased recoverable energy by 8.8%. This result illustrates that influent wastewater COD strength and the plant capacity may have significant impact on the energy recovery potential. Energy production from a WERF can be enhanced by codigesting sewage sludge with highly biodegradable organic waste. Further analysis shows that specifying an appropriate CHP engine is integral in minimizing the energy losses.